Determination of Shallow Ground Water Table in the Bangkok Clay using Seismic Refraction

Summary The location of the ground water table is a geotechnical parameter of interest in the design considerations of infrastructure founded in Bangkok soft clay. In geotechnical practice, the location of this shallow groundwater table (GWT) is commonly determined by measuring the depth to the water table inside a standpipe piezometer. To map the change of water table over a large area using this traditional procedure, a significant number of standpipe piezometers need to be installed which is both time consuming and costly. In this study, a shallow seismic refraction survey was proposed to detect the water table by applying different geophone spacing and finding the optimal spacing by interpreting the interface between two layers of different velocities as the location of ground water table. The depth to this interface was found by seismic data interpretation to be between 1.6 to 1.8 meters, which matches very well with the water depth measured at 1.8 meters deep inside the standpipe piezometer that is located right in the centre of the survey lines. Furthermore, it was found that survey line setups with 2 meters spacing provided the closest location of water table.